WO2021217474A1

WO2021217474A1 - Bidirectional atmosphere control process and bidirectional atmosphere sintering furnace

Info

Publication number: WO2021217474A1
Application number: PCT/CN2020/087699
Authority: WO
Inventors: 刘鹏; 徐文立; 胡芳
Original assignee: 宁波恒普真空技术有限公司
Priority date: 2020-04-29
Filing date: 2020-04-29
Publication date: 2021-11-04
Also published as: CN112512728A; CN112512728B; JP3241481U

Abstract

Disclosed are a bidirectional atmosphere control process and a bidirectional atmosphere sintering furnace. The invention employs bidirectional atmosphere control, such that differences in size and performance of products in respective regions arising from unidirectional atmosphere control can be compensated for by atmosphere control performed in an opposite direction, thereby enabling products placed in the front and back of a furnace to have uniform size and performance.

Description

Two-way atmosphere control process and two-way atmosphere sintering furnace

Technical field

The invention relates to the technical field of a sintering process and a sintering furnace, in particular to a two-way atmosphere control process and a two-way atmosphere sintering furnace.

Background technique

Powder metallurgy products such as MIM are used in various fields, such as consumer electronics, medical equipment, auto parts, smart wear, hardware tools, optical fiber communications, military supplies, etc., which require high product size and performance. However, the yield rate of full furnace products is low, especially for products that are difficult to burn. There are differences in the size and performance of products sintered from the same furnace, and the yield rate of products needs to be further improved.

The sintering furnace in the prior art mainly has the following air intake methods: 1. The gas is directly filled into the material box; 2. The gas outside the material box is fed by the air inlet valve; 3. The upper and lower safety valves are aired; 4. Intake from the side plate to shorten the air flow stroke. The above types of sintering furnaces only have a one-way air inlet structure, and the gas in the sintering furnace flows in one direction. The furnace body is provided with fixed air inlet and outlet positions. During the degreasing and sintering process, the air inlet is air inlet and the air outlet is air outlet, so that the airflow forms a certain directional flow direction. Because the airflow forms a directional flow direction, the size and performance of the regional products in the flow direction will be different. The main reasons are the following three points:

1. The influence of components (impurities) in the gas. The gas contains impurities such as moisture. When the gas flow passes through the product, the moisture and other impurities in the gas will react with the product, which will affect the product. The impact will become smaller and smaller, and there will be differences before and after the product.

2. The influence of volatile matter in the product. For example, in the pre-degreasing process, during the heating process, the adhesive in the product will volatilize from the product, and then enter the air outlet along the direction of the airflow, which will form the volatiles from the previous product and run to the back. , Adhere to the surface of the back product, forming the difference between the front and back products.

3. The influence of gas flow, velocity and flow status. The flow rate and flow rate of the gas flowing through the product near the air inlet position are greater than the flow rate and flow rate of the gas flowing through the product near the air outlet position, and the greater the distance, the more obvious. The airflow passes between the material plate and the material plate. After the airflow passes through a straight line, turbulence will appear. The more the airflow will wash out the product, the smaller the degree of erosion of the product, showing regional product differences. In addition, the air outlet plays a throttling effect, and the carbon potential distribution of the product near the air outlet is often obvious (more carbon content).

Summary of the invention

The purpose of the present invention is to provide a two-way atmosphere control process and a two-way atmosphere sintering furnace to solve the technical problem of large differences in product size and performance caused by the use of one-way atmosphere control in the prior art.

In order to achieve the above objectives, the present invention provides the following solutions:

The invention discloses a two-way atmosphere control process, which includes a preliminary process, a sintering process and a later process. The sintering process includes the following steps:

Step A: Fill the material box with process gas to form a positive flow of gas;

Step B: Fill the material box with process gas to form a reverse flow of gas.

Preferably, the sintering process further includes the following steps:

Step C _A , vacuum in the material box to form a positive flow of gas;

Step C _B. Vacuum in the material box to form a reverse flow of gas.

The invention also discloses a two-way atmosphere sintering furnace, which has a forward atmosphere control structure. The forward atmosphere control structure includes a forward air inlet structure and a forward air outlet structure. The gas flows into the material box from the forward air inlet structure. And it flows out of the material box from the forward air outlet structure to form a forward flow of gas, and also has a reverse atmosphere control structure. The reverse atmosphere control structure has a reverse air inlet structure and a reverse air outlet structure, and the gas flows in from the reverse air inlet structure. And it flows out from the reverse air outlet structure to form a reverse flow of gas.

Preferably, the forward air intake structure is a forward air intake pipe, one end of the forward air intake pipe is located outside the sintering furnace, and the other end of the forward air intake pipe is in communication with the material box in the sintering furnace. The forward air outlet structure is a forward air outlet pipe, one end of the forward air outlet pipe is located outside the sintering furnace, and the other end of the forward air outlet pipe is in communication with the material box in the sintering furnace;

The reverse air inlet structure is a reverse air inlet pipe, the reverse air inlet pipe is a branch pipe of the forward air outlet pipe, the reverse air outlet structure is a reverse air outlet pipe, and the reverse air outlet pipe is a branch pipe of the forward air inlet pipe .

Preferably, the forward air inlet structure is an air inlet valve, the air inlet valve is fixed on the material box, the forward air outlet structure is a forward air outlet pipe, and one end of the forward air outlet pipe is located outside the sintering furnace , The other end of the forward gas outlet pipe is in communication with the material box in the sintering furnace;

The reverse air intake structure is a reverse air intake pipe, the reverse air intake pipe is a branch pipe of the forward air outlet pipe, and the reverse air outlet structure is a splicing gap and a door panel gap on the material box.

Preferably, the positive air intake structure is a safety valve, a splicing gap on the material box, and a door panel gap on the material box, the safety valve is fixed on the material box, and the positive air outlet structure is a positive air outlet pipe, One end of the forward air outlet pipe is located outside the sintering furnace, and the other end of the forward air outlet pipe is in communication with the material box in the sintering furnace;

Preferably, the forward air intake structure is an opening on the side plate of the material box, the forward air outlet structure is a forward air outlet pipe, one end of the forward air outlet pipe is located outside the sintering furnace, and the forward air outlet pipe The other end of the sintering furnace is connected with the material box in the sintering furnace;

The reverse air intake structure is a reverse air intake pipe, the reverse air intake pipe is a branch pipe of the forward air outlet pipe, and the reverse air outlet structure is an opening on a side plate of the material box.

Compared with the prior art, the present invention has achieved the following technical effects:

Through the two-way atmosphere control, the present invention allows the difference in the product size and performance of each region in the flow direction in the one-way atmosphere control to be supplemented by the opposite direction atmosphere control, so that the size and performance of the product are uniform before and after.

Description of the drawings

In order to explain the embodiments of the present invention or the technical solutions in the prior art more clearly, the following will briefly introduce the drawings that need to be used in the embodiments. Obviously, the drawings in the following description are only some of the present invention. Embodiments, for those of ordinary skill in the art, without creative work, other drawings can be obtained based on these drawings.

Figure 1 is a temperature process curve of a sintered product using the bidirectional atmosphere control process of this embodiment;

Figure 2 is a comparison diagram of the carbon potential distribution curves of products with one-way atmosphere control and two-way atmosphere control after sintering;

FIG. 3 is a schematic diagram of a structure of the two-way atmosphere sintering furnace of this embodiment;

4 is a schematic diagram of another structure of the two-way atmosphere sintering furnace of this embodiment;

FIG. 5 is a schematic diagram of another structure of the two-way atmosphere sintering furnace of this embodiment;

6 is a schematic diagram of another structure of the two-way atmosphere sintering furnace of this embodiment;

Description of reference signs: 1 furnace body; 2 material box; 3 forward air inlet pipe; 4 forward air outlet pipe; 5 reverse air inlet pipe; 6 reverse air outlet pipe; 7 air inlet valve; 8 safety valve.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

In order to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

This embodiment provides a two-way atmosphere control process, which includes a pre-process GI, a sintering process GII, and a post-process GIII. The sintering process is more complicated. This embodiment only describes the content related to the gas flow, and the other content of the sintering process can refer to the prior art. The sintering process GII includes the following steps:

Step A: Fill the material box 2 with process gas to form a positive gas flow;

Step B: Fill the material box 2 with process gas to form a reverse flow of gas.

In this embodiment, on the basis of the one-way atmosphere control in the prior art, the reverse-direction atmosphere control is added, so that products with insufficient atmosphere in the previous one-way atmosphere control process can be supplemented, especially products with serious deviations in size and carbon content near the original gas outlet level. , Has played a very good effect, the whole furnace product is sintered, and the size is very uniform. The original one-way atmosphere control is defined as the forward atmosphere control, and the reverse atmosphere control is defined as the reverse atmosphere control.

In addition to the process of filling the material box 2 with gas, the process of vacuuming the material box 2 in the vacuum sintering process also involves the flow of gas. Therefore, in order to further improve the uniformity of the size and performance of the product, the sintering process of this embodiment further includes the following steps:

Step C _A , vacuum inside the material box 2 to form a positive flow of gas;

Step C _B , vacuum in the material box 2 to form a reverse flow of gas.

In a specific embodiment, the step A can be made, Step B continuously, so that steps C _A, C _B continuously Step; Step C _A can be inserted and / or Step C _B between step A and step B. Incidentally, the present embodiment referred to as the forward flow and reverse flow opposite to the flow direction, the same as in Step C _A gas stream of step A in the direction of the present embodiment, the same gas flow direction in the step B and step C _B of the present embodiment .

Specifically, the pre-process G I is mainly a basic process under the premise of heating, such as a degreasing process (if there is no degreasing process, it can be directly heated and kept warm to prepare for direct sintering of the product). The temperature range of the preliminary step GI is from room temperature to 700°C, and preferably from room temperature to 600°C. The latter process GⅢ is mainly the basic process under the premise of cooling, and it is immediately after the end of the sintering process GII, such as the cooling process. The temperature range of the post-process GIII is: the temperature is lowered from 1400°C, preferably from 1200°C. The temperature range during the sintering process GII is 600° C. to 1600° C., preferably 600° C. to 1400° C., including a heating stage, a holding stage and a cooling stage, and the heating stage includes a linear heating and a stepped heating.

Embodiment, the furnace is charged with process gas or nitrogen or argon or a mixture of hydrogen gas, the step A, step B, and the pressure and flow rate within the inflatable Step C _A and C _B in the hopper Step 2 embodiment, can be kept constant The value may also be a variable value, which can be selected by those skilled in the art according to actual needs.

The pressure value in the furnace of Step A and Step B is 0.01 Pa to 1000 KPa, preferably 1 KPa to 100 KPa.

The inflation flow value of step A and step B is 1L/min-500L/min, preferably 1L-200L/min.

Figure 1 is a temperature process curve of MIM products in a sintering furnace. In Figure 1, A1, A2, and A3 are the first, second, and third forward inflation respectively, and so on; B1, B2, B3 They are the first, second, third reverse inflation, and so on. C1 representative of a vacuum process, comprising a first step of Step C _A and C _B. Figure 2 is a comparison diagram of the carbon potential distribution curves of MIM products after sintering in a unidirectional atmosphere and a bidirectional atmosphere. It can be seen that the bidirectional atmosphere control greatly improves the carbon content distribution deviation problem compared to the unidirectional atmosphere control.

This embodiment also provides a two-way atmosphere sintering furnace, which has a forward atmosphere control structure (or one-way atmosphere control structure) commonly used in existing sintering furnaces. The forward atmosphere control structure includes a forward air inlet structure and a forward air outlet structure. Structure, the gas flows into the material box 2 from the positive air inlet structure and flows out of the material box 2 from the positive air outlet structure, forming a positive flow of gas. This embodiment adds a reverse atmosphere control structure on the basis of the prior art. The reverse atmosphere control structure has a reverse air intake structure and a reverse air output structure. Gas flows in from the reverse air intake structure and flows out from the reverse air output structure to form a reverse gas flow. . Depending on the type of sintering furnace, the reverse airflow control structure can have many forms, as long as it can form a reverse airflow opposite to the forward airflow. The following is an example of the reverse atmosphere control structure for four common sintering furnace structures. But it is not limited to the following four layout forms. For example, in the following four structures, the reverse air inlet pipe 5 is a branch of the forward air outlet pipe 4, but those skilled in the art can also make one end of the reverse air inlet pipe 5 located outside the sintering furnace, and the other end of the reverse air inlet pipe 5 is connected to the sintering furnace. The inner tank 2 is connected, and the reverse air inlet pipe 5 is arranged adjacent to the forward air outlet pipe 4, so that the outlet of the forward airflow is very close to the inlet of the reverse airflow, and the two-way atmosphere control can also be realized.

As shown in Fig. 3, it is a sintering furnace structure in which the material box 2 (or muffle) is directly filled with gas. In Fig. 3, the forward air intake structure is a forward air intake pipe 3. One end of the forward air intake pipe 3 is located outside the furnace body 1 of the sintering furnace, and the other end of the forward air intake pipe 3 is connected with the material box 2 in the sintering furnace. The forward air outlet structure is a forward air outlet pipe 4, one end of the forward air outlet pipe 4 is located outside the furnace body 1 of the sintering furnace, and the other end of the forward air outlet pipe 4 is connected with the material box 2 in the sintering furnace;

The reverse air inlet structure is a reverse air inlet pipe 5, the reverse air inlet pipe 5 is a branch pipe of the forward air outlet pipe 4, the reverse air outlet structure is a reverse air outlet pipe 6, and the reverse air outlet pipe 6 is a branch pipe of the forward air inlet pipe 3.

As shown in FIG. 4, it is a sintering furnace structure in which gas enters the material box 2 through the air inlet valve 7 on the material box 2. In Figure 4, the positive air intake structure is an air intake valve 7, which is fixed on the material box 2, and the forward air output structure is a forward air outlet pipe 4, and one end of the forward air outlet pipe 4 is located in the furnace body of the sintering furnace. 1. Outside, the other end of the forward gas outlet pipe 4 is connected with the material box 2 in the sintering furnace;

The reverse air inlet structure is a reverse air inlet pipe 5, the reverse air inlet pipe 5 is a branch pipe of the forward air outlet pipe 4, and the reverse air outlet structure is a splicing gap on the material box 2 and a door panel gap.

As shown in FIG. 5, it is a sintering furnace structure in which gas enters the material box 2 through the safety valve 8 on the material box 2 and the gap on the material box 2. In Figure 5, the positive air intake structure is the safety valve 8, the splicing gap on the material box 2, and the door panel gap on the material box 2. The safety valve 8 is fixed on the material box 2, and the positive air outlet structure is the positive air outlet pipe 4. , One end of the forward air outlet pipe 4 is located outside the furnace body 1 of the sintering furnace, and the other end of the forward air outlet pipe 4 is connected with the material box 2 in the sintering furnace;

As shown in FIG. 6, it is a sintering furnace structure in which gas enters the material box 2 through the opening on the side plate of the material box 2. In Figure 6, the forward air intake structure is an opening on the side plate of the material box 2, and the forward air output structure is a forward air outlet pipe 4. One end of the forward air outlet pipe 4 is located outside the furnace body 1 of the sintering furnace, and the forward air outlet pipe The other end of 4 is connected with the material box 2 in the sintering furnace;

The reverse air intake structure is a reverse air intake pipe 5, the reverse air intake pipe 5 is a branch pipe of the forward air outlet pipe 4, and the reverse air outlet structure is an opening on the side plate of the material box 2.

The following is the sintering data using the sintering furnace shown in Figure 5 with a handle made of 316 material. Table 1 shows the product size distribution and CPK obtained under one-way atmosphere control, and Table 2 shows the product size distribution and CPK obtained under two-way atmosphere control.

Table 1

Table 2

When evaluating the performance of a sintering furnace, the standard deviation and CPK are the main indicators. Standard deviation refers to the uniformity of fluctuations in all dimensions, and the smaller the value, the better. CPK refers to a measure of production feasibility, the benchmark value is 1.33, the larger the value, the better. The comparison shows that the use of the two-way atmosphere control process effectively improves the shortcomings of the one-way atmosphere control process.

In this specification, specific examples are used to describe the principle and implementation of the present invention. The description of the above examples is only used to help understand the method and core idea of the present invention; at the same time, for those of ordinary skill in the art, according to this The idea of the invention will change in the specific implementation and the scope of application. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

A two-way atmosphere control process, including a preliminary process, a sintering process, and a later process, characterized in that the sintering process includes the following steps:

Step A: Fill the material box with process gas to form a positive flow of gas;

Step B: Fill the material box with process gas to form a reverse flow of gas.
The two-way atmosphere control process according to claim 1, wherein the sintering process further comprises the following steps:

Step C A , vacuum in the material box to form a positive flow of gas;

Step C B. Vacuum in the material box to form a reverse flow of gas.
A two-way atmosphere sintering furnace has a positive atmosphere control structure. The positive atmosphere control structure includes a forward gas inlet structure and a positive gas outlet structure. The material box flows out of the gas outlet structure to form a forward flow of gas. It is characterized in that it also has a reverse atmosphere control structure. The reverse atmosphere control structure has a reverse gas inlet structure and a reverse gas outlet structure. The gas flows out from the reverse air outlet structure to form a reverse flow of gas.
The two-way atmosphere sintering furnace according to claim 3, wherein the forward air inlet structure is a forward air inlet pipe, one end of the forward air inlet pipe is located outside the sintering furnace, and the other One end is in communication with the material box in the sintering furnace, the forward air outlet structure is a forward air outlet pipe, one end of the forward air outlet pipe is located outside the sintering furnace, and the other end of the forward air outlet pipe is connected to the material in the sintering furnace. Box connection

The reverse air intake structure is a reverse air intake pipe, the reverse air intake pipe is a branch pipe of the forward air outlet pipe, or the reverse air intake pipe and the forward air outlet pipe are independent pipelines and are arranged adjacently, so The reverse air outlet structure is a reverse air outlet pipe, and the reverse air outlet pipe is a branch pipe of the forward air inlet pipe, or the reverse air outlet pipe and the forward air inlet pipe are independent pipelines and are arranged adjacently.
The two-way atmosphere sintering furnace according to claim 3, wherein the positive air inlet structure is an air inlet valve, the air inlet valve is fixed on the material box, and the positive air outlet structure is a positive air outlet pipe , One end of the forward gas outlet pipe is located outside the sintering furnace, and the other end of the forward gas outlet pipe is in communication with the material box in the sintering furnace;

The reverse air intake structure is a reverse air intake pipe, the reverse air intake pipe is a branch pipe of the forward air outlet pipe, or the reverse air intake pipe and the forward air outlet pipe are independent pipelines and are arranged adjacently, so The reverse air outlet structure is the splicing gap on the material box and the door panel gap.
The two-way atmosphere sintering furnace according to claim 3, wherein the positive air intake structure is a safety valve, a splicing gap on the material box, and a door panel gap on the material box, and the safety valve is fixed on the material box , The positive gas outlet structure is a positive gas outlet pipe, one end of the positive gas outlet pipe is located outside the sintering furnace, and the other end of the positive gas outlet pipe is in communication with the material box in the sintering furnace;

The reverse air intake structure is a reverse air intake pipe, the reverse air intake pipe is a branch pipe of the forward air outlet pipe, or the reverse air intake pipe and the forward air outlet pipe are independent pipelines and are arranged adjacently, so The reverse air outlet structure is the splicing gap on the material box and the door panel gap.
The two-way atmosphere sintering furnace according to claim 3, wherein the positive air inlet structure is an opening on the side plate of the material box, the forward air outlet structure is a forward air outlet pipe, and the forward air outlet pipe One end of the sintering furnace is located outside the sintering furnace, and the other end of the forward gas outlet pipe is connected to the material box in the sintering furnace;

The reverse air intake structure is a reverse air intake pipe, the reverse air intake pipe is a branch pipe of the forward air outlet pipe, and the reverse air outlet structure is an opening on a side plate of the material box.